Shield mounting arrangement for a vacuum circuit interrupter



Aug. 7, 1962 G. POLINKO, JR 3,048,681

SHIELD MOUNTING ARANGEMENT FOR A VACUUM CIRCUIT INTERRUPTER FiledAug. 11, 1960 Inventor: George Pol inko, Jn,

b5 Attorney.

United States Patent ()filice 3,048,681 Patented Aug.'7, 1962 3,048,681 SHIELD MOUNTING ARRANGEMENT FOR A VACUUM CIRCUIT INTERRUPTER George Poliniro, Jr., Levittown, Pa., assignor to General Electric Company, a corporation of New York Filed Aug. 11, 1960, Sen-No. 48,907 1 Claim. (Cl. 200-144) 1 This invention relates to a vacuum-type circuit interrupter and, more particularly, to an improved shielding arrangement for protecting the insulation of the interrupter against the build-up of metallic coatings thereon. In a vacuum circuit interrupter, the metallic vapors that are produced by arcing tend to condenseon the insulating surfaces of the interrupter and, hence, to form metallic coatings which impair the insulating properties of such surfaces. For protecting these surfaces against such metal deposition, a shielding arrangement of the general type disclosed and claimed in US. Patent No. 2,892,- 9 11Crouch, assigned to the assignee of the present invention, has been found effective. Such shielding arrangement comprises a generally tubular metallic shield surrounding the arcing gap between the usual electrodes of the interrupter and electrically isolated from both electrodes and from ground. This electrically isolated shield is physically located between the arcing gap and the internal surface of the usual insulating casing for the interrupter and acts to intercept and condense those metallic vapors traveling toward the insulating surface from the arcing gap.

The supporting arrangements that have been proposed for such shields have either been unduly expensive and complicated or have been diflicult to assemble. arrangement, for example, has required a supporting plate One such extending radially outward from the shield through the surrounding insulating casing. This has necessitated making the insulating casing in two parts and has involved two relatively expensive glass-to-metal seals on opposite sides of the supporting plate. Another supporting arrangement that has been proposed includes a groove formed in the insulating casing for receiving radiallyoutwardly projecting tabs carried by the shield. This arrangement is subject to the disadvantage that it is difficult to assemble since the tabs cannot easily be positioned adjacent the groove and then bent into position without scratching or otherwise impairing the internal surface of the insulating housing and is subject to the additional disadvantage that. thegroove in the usual casing tends to unduly weaken thecasing from a'mechanical strength standpoint.

' Accordingly, an object of my invention is to provide 'a vacuum circuit interrupter with an improved shieldsupporting arrangement that is simple and inexpensive, is easily assembled with little risk of impairing the internal surface of the insulating housing, and does not unduly detract from the mechanical strength of the insulating casing.

Another object is to construct this shield-supporting arrangement in such a manner that it requires no glass-tometal seals to prevent leakage into the vacuum envelope.

. Another object is to construct the shield supporting arrangement in such a manner that the metallic shield can expand and contract in response to temperature changes without unduly'stressing the surrounding insulating housing. i

In carrying out my invention in one form, I provide in the casing in circumferentially spaced-apart relationship and are bonded thereto. The pins extend in a generally radial direction relative to the casing and extend only partially through the casing. A plurality of tabs are secured to the outer periphery of the tubular shield in circumferential alignment with certain of the radially-extending pins. These tabs are provided with apertures that receive the pins and thus support the shield on the pins. In a preferred form of the invention the apertures are made appreciably larger than the pins to permit free movement of the tabs relative to the pins in response to thermally induced expansion and contraction of the metallic shield.

For a better understanding of my invention, reference may be had to the following description taken in conjunction with the accompanying drawing, wherein:

FIG. 1 is a cross-sectional view of a vacuum-type circuit interrupter embodying my invention in one form.

FIG. 2 is a cross-sectional view taken along the line 2-2 of FIG. 1.

FIG. 3 is a perspective view of a portion of the interrupter of FIGS. 1 and 2.

Referring now to the interrupter of FIG. 1, there is shown a highly-evacuated envelope 10 comprising a tubular casing 11 of insulating material, such as a suitable glass, and a pair of metallic end caps 12 and 13 closing off the ends of the casing. Suitable seals 14 are provided between the end caps and the casing to render the envelope 10 vacuum-tight.

Located within the envelope is a pair of separable electrodes, or rod contacts, 17 and 18 shown by solid lines in the closed-circuit position. The electrode 17 is a stationary electrode suitably united to the upper end cap 12, whereas the electrode 18 is a movable electrode suitably mounted for vertical movement and projecting through an opening in the lower end cap 13. A flexible metallic bellows 20 interposed between the end cap 13 and the movable electrode 18 provides a seal about the movable electrode and allows for vertical movement thereof without imparing the vacuum inside the interrupter. As shown on the drawing, the bellows20 is sealingly secured at its respective opposite ends to the electrode 18 and the end cap 13.

Coupled to the lower end of the movable electrode 18, I provide suitable actuating means (not shown) which is capable of driving the electrode rapidly downwardly from its solid-line position of FIG. 1 to its dotted-line position 55 resulting are, though quickly extinguished, vaporizes some of the metal of the electrodes.

In order to prevent this metallic vapor from condensing on the internal insulating surfaces of the casing 11, there is provided a metallic shield 25 which corresponds in certain respects to a similarly designated shield in the aforesaid Crouch application. This metallic shield 25 is of a generally tubular configuration and extends along the length of the casing 11 for substantial distances on opposite sides of the gap between the electrodes. The shield 25 is electrically isolated from both of the electrodes 17 and 18 and, preferably, is also isolated from ground, or in other words, is at a floating potential relative to the two electrodes.

This electrical isolation between the shield 25 and the electrodes 17 and 18 is achieved by mounting the shield 25 on the insulating casing adjacent the central region of the shield and by spacing the shield radially inward from the tubular insulating casing 11 at all points on opposite sides of the centrally disposed mounting region.

Essentially all straight line paths extending from the general region of the arcing gap to the insulating casing 11 are intercepted by the floating central shield 25. As a result of this relationship, substantially all metallic particles that are liberated from the electrodes by arcing are intercepted and captured either by the shield 25 or the end caps 12 and 13 before they can reach the internal surfaces of the casing 11.

The shield-supporting arrangement comprises a plurality of metallic pins 30 circumferentially spaced about the casing 11 and extending radially inward from the casing 11. These pins 30 are embedded in the casing 11= and are bonded to the glass of the casing. The pins 30 are incorporated into the casing 11 during the manufacturing process by any suitable procedure, such as first heating the casing to a plastic condition in its central region and then forcing the pins into the plastic glass. The pins 30 are constructed of a suitable metal that has substantially the same coefiicient of thermal expansion as the glass so as to prevent the glass from being unduly stressed or the pins loosened by expansion and contraction of the parts in response to temperature changes.

The shield-supporting arrangement further comprises a plurality of U-shaped tabs 32, each having an inner leg 32a and an outer leg 32b. The inner leg 32a of each tab is welded to the outer periphery of the shield 25 in a position wherein the tabs are disposed in circumferential alignment with the pins 30. The outer leg of each tab 32 has an aperture 34 therein for receiving one of the pins 30. Prior to assembly of the shields 25 inside the casing 11, at least some of the tabs are slightly flattened, as by bending the outer leg 32b of a tab toward the shield 25. The shield is then positioned inside the casing 11 with the apertures 34 of the tabs in alignment with the pins 38, after which the flattened tabs are expanded into their position of FIG. 1 so that the aperture of each tab receives its corresponding pin 30. The shield is then supported on the pins 30 in the manner shown in FIG. 1. In a preferred form of my invention, I use six tabs equally-spaced about the periphery of the shield 25, though a greater or lesser number may be used if desired.

Preferably, the apertures 34 that receive the pins 30 are appreciably larger than the pins 30. The resulting clearance between the pins 30 and the apertures 34 allows the shield, in response to temperature changes, to contract and expand independently of the casing 11 without stressing the casing 11 inasmuch as the tabs 32 are free to. move relative to the pins 30 during such expansion and contraction. Thus, the casing is protected from mechanical stresses that might otherwise result from unequal expansion and contraction of the shield 25 and the casing 11.

As an added measure of protection against the transmission of objectionably high forces to the casing 11, the yieldability of the tabs can be relied upon to lessen the magnitude of the forces transmitted to the casing 11. If the yieldability of the tabs is to be relied upon for this protection, the apertures 34 can be made smaller than where clearance between the pins 30 and the apertures 34 is alone relied upon. I

It is to be noted that the pins 30 extend only partially through the casing 11, the outer peripheral portion of the casing remaining imperforate. Thus, there is no significant possibility that an imperfect bond between the pins 30 and the glass of the casing will result in a leak from the surrounding atmosphere along the junction between, the pin and the casing. It is to be further noted that the disclosed shield supporting arrangement permits the casing 11 to be made of a single integral part, rather than in two parts joined together with glass-to-metal seals, as has been the case with some prior arrangements.

Also, the imperforate nature of the outer peripheral portion of the insulating casing 11 contributes to increased creepage paths along this outer surface in comparison to those available with equal length casings that include metallic parts extending therethrough.

The fact that the pins 30 are bonded to the surrounding glass results in a mechanically stronger construction than one in which an open groove or hole is present in the casing since both tensile and compressive forces in the disclosed casing can be transmitted to the pin through the bond, thus reducing mechanical stress concentrations in the material of the casing. Preferably, the area of the bond is increasedby providing the internal surface of the casing 11 with an annular emboss-ment 36 for receiving the pins 30. The increased bonding area made available by this embossment contributes to a stronger bond and a stronger casing (11). v I

Where the advantages gained from having a casing with an imperforate outer periphery are not of controlling importance, 1 can utilize for practicing my invention in its broader aspects aconstruction identical to that disclosed but with the pins 30 extending entirely through the casing 11.

While I have shown and described a particular embodiment of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from my invention in its broader aspects and I, therefore, intend in the appended claim to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

A vacuums-type circuit interrupter comprising an evacuated tubular casing of insulating material, a pair of electrodes disposed within said casing and having a spaced-apart position defining an arcing gap therebetween, a generally tubular metallic shield surrounding said arcing gap and extending along the length of said casing for substantial distances on opposite sides of said arcing gap, said metallic shield being electrically isolated from said electrodes and having its end portions radially-spaced from said casing, a plurality of metallic pinsembedded in said casing in circumferentially spaced-apart relationship and bonded thereto, said pins extending in a generally radial direction relative to said casing and extending only partially through said casing, a plurality of circumferentially spaced generally U-shaped tabs each hav ing spaced-apart inner and outer legs, the inner of said legs being attached to the outer periphery of said shield and the outer of said legs being located radially outward from said other leg, said tabs being secured to the outer periphery of said shield in circumferential alignment with certain of said radially extending pins, and means for supporting said tabs on said pins comprising apertures in said outer legs receiving said pins, said apertures being appreciably larger than said pins to permit free movement of said tabs relative to said pins in response to thermally induced expansion and contraction of said metallic shield.

References Cited in the file ofthis patent UNITED STATES PATENTS 

